Universe - Orbits of the planets around the Sun
978-3-14-100890-6 | Page 11 | Ill. 9
Overview
Our solar system was formed about 4.6 billion years ago from an interstellar cloud of gas and dust that contracted under the influence of its own gravity. Almost all the matter gathered in the centre, creating the Sun as a star. Only a small part of the matter formed around it a disc flattened by its rotation, from which the other bodies of the solar system were formed.
This Illustration shows the orbits of the planets to scale - including Pluto - with their distances to the Sun and with information on their orbital periods around the Sun.
Celestial bodies of our solar system
Besides the Sun, there are these celestial bodies dependent on it in our solar system: • the eight large planets with their moons, which together make up only 1.34 per cent of the mass of the solar system, of which 92 per cent is accounted for by the giants Jupiter and Saturn, • the minor planets or planetoids, most of which are in a belt between Mars and Jupiter, and • the comets, the majority of which are located in the so-called Kuiper belt far outside Pluto's orbit or in the even more distant Oort cloud.
The mass of all minor planets and comets is less than 0.1 per cent of the entire solar system. The sizes of the Sun and planets are shown here to scale. The inner planets Mercury, Venus, Earth and Mars are Earth-like with their rocky structure and relatively high densities of 3.9 to 5.6 grams per cubic centimetre. The gas planets Jupiter, Saturn, Uranus and Neptune, apart from their small rocky core, consist mainly of hydrogen and helium and reach densities of 0.7 to 1.6 grams per cubic centimetre. On Mercury, there are extreme day-night temperature differences due to the lack of an atmosphere.
While the temperature on Venus is about 500°C due to its proximity to the Sun and an extreme greenhouse effect, it is mostly below freezing on Mars and below minus 150°C on Jupiter. These temperatures are measured in the lower cloud layer because gas planets have no solid surface and the gas changes to a liquid state with depth.
Pluto has been taken out of the series of large planets: It is located, along with several other recently discovered similar objects, near the Kuiper belt of comets. Its structure also resembles that of a comet with a conglomeration of ices containing methane, ammonia, carbon dioxide, etc., in addition to water and rocks.
